适合教学课件的背景图片
http://image.baidu.com/i?tn=baiduimage&ct=201326592&lm=-1&cl=2&fr=ala0&word=%BD%CC%D1%A7%BF%CE%BC%FE%B1%B3%BE%B0%CD%BC%C6%AC#
http://image.baidu.com/i?tn=baiduimage&ct=201326592&lm=-1&cl=2&fr=ala0&word=%BD%CC%D1%A7%BF%CE%BC%FE%B1%B3%BE%B0%CD%BC%C6%AC#